How does filing tuition for an entire year (2018-2019 school year) work? I have tuition for the winter session (2018) that I forgot to file in the previous year (2019)

If you have tuition from 2018 that you didn't claim that year, you'll need to go back and adjust your return for that year to include it. You may want to double check your Notice Of Assessment for 2018 first, as the CRA may have added it themselves.

You can make changes after you have filed your tax return through the Canada Revenue Agency (CRA) or through ReFILE. This FAQ has more information: https://turbotax.community.intuit.ca/community/tax-return-amendment/help/i-have-filed-my-tax-return-can-i-still-make-changes/00/873608